<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Scientific Calculator</title>

<SCRIPT LANGUAGE="JavaScript">
function addChar(input, character) {
	if(input.value == null || input.value == "0")
		input.value = character
	else
		input.value += character
}

function cos(form) {
	form.display.value = Math.cos(form.display.value);
}

function sin(form) {
	form.display.value = Math.sin(form.display.value);
}

function tan(form) {
	form.display.value = Math.tan(form.display.value);
}

function sqrt(form) {
	form.display.value = Math.sqrt(form.display.value);
}

function ln(form) {
	form.display.value = Math.log(form.display.value);
}

function exp(form) {
	form.display.value = Math.exp(form.display.value);
}

function deleteChar(input) {
	input.value = input.value.substring(0, input.value.length - 1)
}

function changeSign(input) {
	if(input.value.substring(0, 1) == "-")
		input.value = input.value.substring(1, input.value.length)
	else
		input.value = "-" + input.value
}

function compute(form) {
	form.display.value = eval(form.display.value)
}

function square(form) {
	form.display.value = eval(form.display.value) * eval(form.display.value)
}

function checkNum(str) {
	for (var i = 0; i < str.length; i++) {
		var ch = str.substring(i, i+1)
		if (ch < "0" || ch > "9") {
			if (ch != "/" && ch != "*" && ch != "+" && ch != "-" && ch != "."
				&& ch != "(" && ch!= ")") {
				alert("invalid entry!")
				return false
				}
			}
		}
		return true
}
</SCRIPT>

</head>
<body>
<FORM NAME="sci-calc">
<TABLE CELLSPACING="0" CELLPADDING="1">
<TR>
<TD COLSPAN="5" ALIGN="center"><INPUT NAME="display" VALUE="0" SIZE="28" MAXLENGTH="25"></TD>
</TR>
<TR>
<TD ALIGN="center"><INPUT TYPE="button" VALUE=" exp " ONCLICK="if (checkNum(this.form.display.value)) { exp(this.form) }"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  7  " ONCLICK="addChar(this.form.display, '7')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  8  " ONCLICK="addChar(this.form.display, '8')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  9  " ONCLICK="addChar(this.form.display, '9')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="   /   " ONCLICK="addChar(this.form.display, '/')"></TD>
</TR>
<TR>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="   ln   " ONCLICK="if (checkNum(this.form.display.value)) { ln(this.form) }"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  4  " ONCLICK="addChar(this.form.display, '4')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  5  " ONCLICK="addChar(this.form.display, '5')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  6  " ONCLICK="addChar(this.form.display, '6')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="   *   " ONCLICK="addChar(this.form.display, '*')"></TD>
</TR>
<TR>
<TD ALIGN="center"><INPUT TYPE="button" VALUE=" sqrt " ONCLICK="if (checkNum(this.form.display.value)) { sqrt(this.form) }"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  1  " ONCLICK="addChar(this.form.display, '1')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  2  " ONCLICK="addChar(this.form.display, '2')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  3  " ONCLICK="addChar(this.form.display, '3')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="   -   " ONCLICK="addChar(this.form.display, '-')"></TD>
</TR>
<TR>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  sq  " ONCLICK="if (checkNum(this.form.display.value)) { square(this.form) }"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="  0  " ONCLICK="addChar(this.form.display, '0')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="   .  " ONCLICK="addChar(this.form.display, '.')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE=" +/- " ONCLICK="changeSign(this.form.display)"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="   +  " ONCLICK="addChar(this.form.display, '+')"></TD>
</TR>
<TR>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="    (    " ONCLICK="addChar(this.form.display, '(')"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="cos" ONCLICK="if (checkNum(this.form.display.value)) { cos(this.form) }"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE=" sin" ONCLICK="if (checkNum(this.form.display.value)) { sin(this.form) }"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE=" tan" ONCLICK="if (checkNum(this.form.display.value)) { tan(this.form) }"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="   )   " ONCLICK="addChar(this.form.display, ')')"></TD>
</TR>
<TR>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="clear" ONCLICK="this.form.display.value = 0 "></TD>
<TD ALIGN="center" COLSPAN="3"><INPUT TYPE="button" VALUE="backspace" ONCLICK="deleteChar(this.form.display)"></TD>
<TD ALIGN="center"><INPUT TYPE="button" VALUE="enter" NAME="enter" ONCLICK="if (checkNum(this.form.display.value)) { compute(this.form) }"></TD>
</TR>
</TABLE>
</FORM>

</body>
</html>